The present invention relates generally to Internet Protocol (IP) telephony including voice over IP and more specifically to IP telephony applications that terminate with ISUP signaling.
Common channel signaling system number 7 (SS7 or C7) is a global standard for telecommunications defined by the International Telecommunication Union (ITU) and specifically the Telecommunications Standardization Section of the ITU (ITU-T). In essence, the SS7 standard defines the procedures and protocols by which network elements in the public switch telephone network (PSTN) exchange information over a digital signaling network including wireless, e.g. cellular, and wireline call setup, routing and control. The ITU definition of SS7 allows for variance of the procedures and protocols such as those promulgated by the American National Standards Institute (ANSI) and Bell Communications Research (Bellcore) standards used in North America as well as the European Telecommunication Standards Institute (ETSI) standards used in Europe.
Essentially, an SS7 network and the defined protocols are used for implementing call signaling functions including basic call setup management and tear down. In addition, SS7 specifies various wireless services such as personal communication services (PCS), wireless roaming and mobile subscription authentication. Most recently, the SS7 protocol has been used for local number portability (LNP) as well as toll free and toll wireline services. Other services that benefit from the SS7 protocol include enhanced called features such as call forwarding, calling party name and number display and three way calling as well as a wide array of emerging applications standards that provide for efficient and secure worldwide telecommunication.
With an SS7 network, messages are exchanged between network elements over 56 or 64 kilobits per second (kbps) using bi-directional channels called signaling links. Signaling occurs-out-of-band on dedicated channels rather than in-band on voice channels. Compared to in-band signaling, out-of-band signaling provides faster call setup times, more efficient use of voice circuits, and support for intelligent network services which require signaling to network elements without voice trunks. In addition, out-of-band provides for improved control over fraudulent network use. These advantages have made the SS7 protocol a popular choice for voice over Internet Protocol (IP) applications including IP telephony.
The hardware and software functions of the SS7 protocol are divided into functional abstractions called levels. These levels map loosely to the Open Systems Interconnect (OSI) 7-layer model defined by the International Standards Organization (ISO). An ISDN user part (ISUP) defines the protocol used to setup, manage and release trunk circuits that carry voice data between terminating line exchanges, e.g., between a calling party and a called party. In general, ISUP is used for both Integrated Systems Digital Services (ISDN) and non-ISDN calls. However, calls that originate and terminate at the same switch do not use ISUP signaling.
The layers that are used to implement the ISUP stack may be distributed among multiple processors in an SS7 network in order to accomplish the message signaling functions specified in a particular ISUP protocol. For example, a signaling link may need to be allocated based on availability of the element in the PSTN portion of the network or in the SS7 gateway node. Likewise, other setup management and signaling functions may be implemented by the assistance of distributed elements and layered functions within the network.
A technical challenge that exists when ISUP stacks are distributed between multiple processors is the routing of messages to the proper processor and the handling of circuit connections. Present ISUP stack implementations require a dedicated processor from a single vendor or one that has been adapted using fixed signaling protocols that are not easily open to reconfiguration. Thus, an SS7 protocol stack may not support the interface between one layer in a stack and another layer if the interfaces belong to different vendor equipment. The end result may be difficult or impossible integration of network equipment from different vendors into a single network architecture. While distributed ISUP processing is used and available today, only proprietary systems with products from a single vendor or products that have been adapted to be used within a single system are employed.
The present invention provides a mechanism in the form of a thin layer within the SS7 protocol stack that makes it possible for ISUP stacks running on distributed processors to run independently without knowledge regarding its distribution. In this way, any adaptation in the signaling between a message transfer part (MTP) node and an ISUP node can be handled within the added layer. The mechanism permits different vendor elements to use ISUP stacks from different vendors.
According to one embodiment, disclosed is a mechanism for distributing end-to-end call setup and signaling functions among multiple processors in a common channel signaling system. The mechanism includes an array of loosely coupled processors that communicate with each other over connections using a standardized protocol such as the Internet Protocol (IP). A task distribution module is operably coupled to the array and configured to administer failure recovery functions when one of the connections or processors fail. The connections can be configured to provide signaling links for carrying voice data and in one embodiment support signaling system number 7 (SS7).
The task distribution function can be implemented between the MTP layer 3 and the ISUP layer of a SS7 signaling link. In this way some of the processors can be functionally organized as a SS7 gateway while some other processors can be functionally organized as a voice gateway or access server which communicates with the SS7 gateway through a TCP/IP connection.
Further disclosed is a mechanism for internetworking an SS7 gateway and distributed ISUPs residing on separate processors in an Internet Protocol telephony signaling network utilizing common channel signaling system number 7 (SS7). The mechanism includes an operations management module configured to control circuit signaling functions between the SS7 gateway and the distributed ISUPs. A plurality of ISUP messaging functions are implemented in hardware and control the format of both single circuit and group messages distributed between the SS7 processors. The mechanism also includes a connection supervision module that maintains connections between any of the separate processors and is configured so that the operations management module, ISUP messaging functions and connection supervision module together form a protocol stack layer interspersed between the MTP layer 3 and the ISUP layer of the network. The mechanism can include a public switch telephone network coupled to the SS7 gateway through an SS7 signaling link. In one embodiment, the ISUPs include a voice gateway coupled to the SS7 gateway through a TCP/IP communications link. Speech connection channels can be used to couple the voice gateways to the PSTN.